Precursor composition for optical resin, resin for optical use, optical element, and optical article

ABSTRACT

The optical element of the present invention has a first member and a second member which have been joined in close contact, and has n d1 &gt;n d2  and (n F1 −n C1 )&lt;(n F2 −n C2 ), where the first member is formed of a resin having both a benzene ring and a fluorine atom, or the second member is formed of a resin having an alicyclic structure It also makes use of an optic-purpose resin precursor composition prepared by mixing a first resin precursor having n d &lt;1.50 and (n F −n C )&gt;0.003 in an uncured state and a second resin precursor having n d &lt;1.62 and (n F −n C )&gt;0.010.

TECHNICAL FIELD

This invention relates to a close-contact double-layer type diffractiveoptical element and a method for its production, and to an opticalarticle having this element, and an optic-purpose resin precursorcomposition and an optic-purpose resin which-are used in the element.

BACKGROUND ART

In recent years, a technique has been developed in which chromaticaberration is corrected using a diffractive optical element in animaging optical system, and optical materials having a: low refractiveindex and a high dispersion which are favorable for use in it attractnotice. For example, in a close-contact double-layer type diffractiveoptical element consisting of two layers having different opticalcharacteristics, as proposed in Japanese Patent Laid-open PublicationNo. H9-127321, an optical material having a low refractive index and ahigh dispersion is used in one of layers constituting the element.

However, it is known that optical materials have a positive correlationbetween the refractive index and the dispersion. Materials having a lowrefractive index has a small dispersion, and conversely materials havinga high refractive index has a large dispersion. Hence, optical materialshaving a high dispersion though having a low refractive index are verylimited. In fact, materials disclosed in the above publication arealmost inorganic materials, and just only polycarbonates are disclosedas organic materials.

Accordingly, inorganic matter, in particular, a glass is usually used asan optical material in such a close-contact double-layer typediffractive optical element. For example, in Japanese Patent Laid-openPublication No. 2001-235608, a method is disclosed in which aclose-contact double-layer type diffractive optical element is producedusing a low-melting glass.

However, in general, inorganic materials are inferior to organicmaterials in respect of workability and moldability, and also it is noteasy to bring inorganic optical materials into perfect close contactwith each other. In addition, glass materials are necessarily limitedand moreover required to have heat resistance because they are molded ata high temperature. Hence, materials for molds are also limited. Also,because of a high viscosity of glass materials at the time of molding,it has been difficult to materialize sufficient transfer properties.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide aclose-contact double-layer type diffractive optical element which can beproduced with ease and simply in a good precision, a method for itsproduction, an optical article having such an element, an optic-purposeresin precursor composition favorable as a material for the element, andan optic-purpose resin which is a cured product of the composition.

To achieve the above object, first invention in the present applicationprovides an optic-purpose resin precursor composition obtained by mixingat least:

(1) a first resin precursor having a d-line refractive index n_(d) ofless than 1.50 in an uncured state, and having in an uncured state adifference (average dispersion MD) of larger than 0.003 which is foundby subtracting a C-line refractive index n_(C) from an F-line refractiveindex n_(F); and

(2) a second resin precursor having a d-line refractive index n_(d) ofless than 1.62 in an uncured state, and having in an uncured state adifference (average dispersion MD) of larger than 0.010 which is foundby subtracting a C-line refractive index n_(C) from an F-line refractiveindex n_(F).

Incidentally, in the present specification, the resin is meant to be anorganic high-molecular compound. Also, in the present invention, theresin precursor may as well be any of monomers, oligomers, prepolymers,polymers and so forth as long as resins are obtainable by curing.

In the optic-purpose resin precursor composition of the presentinvention, the first resin precursor does not contain any of a benzenering, a sulfur atom, a chlorine atom, a bromine atom and an iodine atom,has at least one of any of an acrylic group, a methacrylic group and avinyl group, and the second resin precursor does not contain any of asulfur atom and a halogen atom, and has at least one of any of anacrylic group, a methacrylic group and a vinyl group. Otherwise, thefirst resin precursor is represented by the following compositionalformula (1) and has at least one polymerizable functional group in themolecule, and the second resin precursor is represented by the followingcompositional formula (2) and has at least one polymerizable functionalgroup in the molecule and at least one benzene ring in the molecule.C_(m1)H_(n1)O_(p1)N_(q1)F_(r1)  (1)wherein m1 and n1 are each an integer of 5 or more, p1 and q1 are eachan integer of 0 or 1 or more and m1 or less, and r1 is an integer of 0or 1 or more and (n1×2) or less.C_(s1)H_(t1)O_(u1)N_(v1)  (2)wherein s1 and t1 are each an integer of 5 or more, and u1 and v1 areeach an integer of 0 or 1 or more and s1 or less.

The present invention further provides an optic-purpose resin obtainedby curing the above optic-purpose resin precursor composition of thepresent invention, an optical element comprising a first member formedof such a resin, and an optical article having this optical element ofthe present invention.

Second invention in the present application provides a diffractiveoptical element which is a close-contact double-layer type diffractiveoptical element having a second member formed of a first resin and afirst member formed of a second resin, joined to the second member inclose contact, where the second member has a d-line refractive indexn_(d1) which is larger than a d-line refractive index n_(d2) of thefirst member, and the second member has an average dispersion MD₁ (thatis, a difference found by subtracting a C-line refractive index n_(C1)of the second member from an F-line refractive index n_(F1) of thesecond member) which is smaller than an average dispersion MD₂ (that is,a difference found by subtracting a C-line refractive index n_(C2) ofthe first member from an F-line refractive index n_(F2) of the firstmember) of the first member;

(1) the first resin having an alicyclic structure in the repeating unit;and/or

(2) the second resin having both a benzene ring and a fluorine atom inthe repeating unit;

and provide an optical article having this close-contact double-layertype diffractive optical element of the present invention.

The present invention also provides a method for producing aclose-contact double-layer type diffractive optical element, which is amethod for producing a close-contact double-layer type diffractiveoptical element having a second member formed of a first resin and afirst member formed of a second resin, joined to the second member inclose contact; the method having the step of molding a compositioncontaining a precursor of the first resin (that is, a fourth resinprecursor) and curing the composition to form the second member; thefirst resin having an alicyclic structure in the repeating unit; and(d-line refractive index n_(d1) of first resin)>(d-line refractive indexn_(d2) of second resin); and (average dispersion MD₁ of firstresin)<(average dispersion MD₂ of second resin).

The present invention further provides a method for producing aclose-contact double-layer type diffractive optical element, which is amethod for producing a close-contact double-layer type diffractiveoptical element having a second member formed of a first resin and afirst member formed of a second resin, joined to the second member inclose contact; the method having the step of molding a compositioncontaining a precursor of the second resin (that is, a third resinprecursor) and curing the composition to form the first member; and(d-line refractive index n_(d1) of first resin)>(d -line refractiveindex n_(d2) of second resin); and (average dispersion MD₁ of firstresin)<(average dispersion MD₂ of second resin).

Incidentally, here;

(average dispersion MD₁ of first resin)=(F-line refractive index n_(F1)of first resin)−(C-line refractive index n_(C1) of first resin); and

(average dispersion MD₂ of second resin)=(F-line refractive index n_(F2)of second resin)−(C-line refractive index n_(C2) of second resin).

Incidentally, the optic-purpose resin precursor composition of theinvention in the present application may further contain a third resinprecursor (that is, a precursor of the second resin) in addition to theabove first resin precursor and second resin precursor. The curedproduct of the optic-purpose resin precursor composition containing thefirst resin precursor and second resin precursor may also be the secondresin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a close-contact double-layer typediffractive optical element in Example 1, where reference numeral 10denotes the close-contact double-layer type diffractive optical element;11, a first member formed of a low refractive-index and high-dispersionoptical material; and 12, a high-refractive-index and low-dispersionoptical material.

FIG. 2 is a sectional view showing a process of producing aclose-contact double-layer type diffractive optical element in Example2.

FIG. 3 is a sectional view showing a process of producing aclose-contact double-layer type diffractive optical element in Example3, where reference numeral 10 denotes the close-contact double-layertype diffractive optical element; 21, a first member; 22, a secondmember; and 23, a base material.

BEST MODES FOR PRACTICING THE INVENTION

Conventionally, optical materials having a low refractive index and ahigh dispersion have been very limited. Accordingly, the presentinventors have made extensive studies so that materials superior inworkability, molderability, adherence and transfer properties can freelybe selected. As the result, they have reached a new finding that thedesired optical characteristics can be obtained by mixing a componenthaving a low refractive index and a component having a high dispersionas long as components having specific characteristics are used, and haveaccomplished the invention in the present application.

In the first invention in the present application, a first component(first resin precursor) having a low refractive index and a secondcomponent (second resin precursor) having a high dispersion are mixed tomaterialize a resin having a high dispersion though having a lowrefractive index. More specifically, the optic-purpose resin precursorcomposition of the first invention in the present application comprisesa first resin precursor having a d-line refractive index n_(d)<1.50 anda dispersion (n_(F)−n_(C))>0.003 in an uncured state, and a second resinprecursor having a d-line refractive index n_(d)<1.62 and a dispersion(n_(F)−n_(C))>0.010 in an uncured state. Incidentally, these resins mayas well be present alone for each, or stand copolymerized.

The first resin precursor is required to have a low d-line refractiveindex (nd<1.50) and also a some high dispersion [(n_(F)−n_(C))>0.003].Such a resin may preferably not contain a benzene ring, a sulfur atomand halogen atoms other than fluorine (a chlorine atom, a bromine atomand an iodine atom), which may give a high refractive index.

Incidentally, the fluorine has the action to lower the refractive index,and hence a compound containing fluorine may as well be used as thefirst resin precursor. However, the fluorine may preferably be in acontent twice or less the total number of hydrogen atoms in themolecule. If fluorine atoms are more than this, the resin obtainedfinally by curing the resin precursor composition in which the secondcomponent has been mixed may have too low dispersion. Also, if fluorineatoms are too many, a low compatibility with the second component mayresult, so that the resin precursor composition and the resin, a curedproduct of the former, may come milky-white. This first resin precursormay preferably have ultraviolet curability or heat curability, and, inorder to materialize this, may preferably contain a polymerizablefunctional group such as an acrylic group, a methacrylic group or avinyl group. Incidentally, this functional group may be alone in themolecule, or present in plurality.

As such a first resin precursor, a compound may be used which isrepresented by the following compositional formula (1), having at leastone polymerizable functional group in the molecule.C_(m1)H_(n1)O_(p1)N_(q1)F_(r1)  (1)wherein m1 and n1 are each an integer of 5 or more, p1 and q1 are eachan integer of 0 or 1 or more and m1 or less, and r1 is an integer of 0or 1 or more and (n1×2) or less. Stated specifically, the first resinprecursor may preferably be a compound represented by any of thefollowing general formulas (3) to (9).

Here, R¹, R³, R⁵, R⁷, R¹² and R¹⁷ are each a hydrogen atom or a methylgroup; R², R⁴ and R⁶ are each a monovalent organic group; R⁸ is adivalent organic group; R⁹ to R¹¹ are each a monovalent organic grouphaving an acrylic group or a methacrylic group; R¹³, R¹⁴ and R¹⁶ areeach a divalent organic group; R¹⁵, R¹⁸ and R¹⁹ are each a monovalentorganic group; a, d and f are each a number of 2 or more to 4 or less;and b, e and g are each a number of 1 or more.

Incidentally, R², R⁴, and R⁸ and R⁶ may each preferably be an organicgroup represented by the compositional formula:C_(m2)H_(n2)O_(p2)N_(q2)F_(r2) (where m2 is an integer of 1 or more, p2and q2 are each an integer of 0 or more, n2 is an integer of 1 or more,and r2 is an integer of 0 or [(n2+5)×2] or less and 1 or more), and R⁹to R¹¹, R¹³ to R¹⁶, R¹⁸, and R¹⁹ may each preferably be made up of C, Hand O.

Compounds favorable for the first invention in the present applicationas this first resin precursor may include, e.g., as the compoundrepresented by the formula (3), 2,2,2-trifluoroethyl methacrylate,2,2,2-trifluoroethyl acrylate, β-(perfluoroethyl)ethyl methacrylate,β-(perfluoroethyl)ethyl acrylate, 1,1,1,3,3,3,-hexafluoroisopropylmethacrylate, 1,1,1,3,3,3,-hexafluoroisopropyl acrylate,2,2,2-trifluoroethyl methacrylate, 2,2,2-trifluoroethyl acrylate,2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3-tetrafluoropropylmethacrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate,2,2,3,4,4,4-hexafluorobutyl methacrylate, octafluoropentyl methacrylate,octafluoropentyl acrylate, methyl methacrylate, methyl acrylate, ethylacrylate, butyl methacrylate, butyl acrylate, isodecyl methacrylate,isodecyl acrylate, lauryl methacrylate, lauryl acrylate,tridecylmethacrylate, tridecyl acrylate, cetylmethacrylate, cetylacrylate, stearyl methacrylate, stearyl acrylate, tert-butylmethacrylate, tert-butyl acrylate, 2-ethylhexyl methacrylate,2-ethylhexyl acrylate, 2-hydrbxybutyl acrylate, 2-hydroxybutylmethacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-methoxybutylacrylate, diethylaminoethyl methacrylate and diethylaminoethyl acrylate.

The compound represented by the formula (4) which is favorable for thefirst invention in the present application may include 2-ethyl2-butyl-propanediol methacrylate, 2-ethyl 2-butyl-propanediol acrylate,1,3-butyleneglycol dimethacrylate, 1,3-butyleneglycol diacrylate,1,6-hexanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,9-nonanedioldimethacrylate, 1,9-nonanediol diacrylate,1,10-decanedioldimethacrylate, 1,10-decanediol diacrylate, neopentylglycol dimethacrylate, neopentyl glycol diacrylate, dipropyleneglycoldimethacrylate, dipropyleneglycol diacrylate and glyceroldimethacrylate.

The compound represented by the formula (5) which is favorable for thefirst invention in the present application may includedimethylaninoethyl methacrylate, 2-ethylhexylcarbitol methacrylate,2-ethylhexylcarbitol acrylate, butoxyethyl methacrylate, butoxyethylacrylate, ethoxydiethyleneglycol methacrylate, ethoxydiethyleneglycolacrylate, lauroxypolyethyleneglycol methacrylate,lauroxypolyethyleneglycol acrylate, polyethyleneglycol methacrylate(a=2, b=2 to 12), polyethyleneglycol acrylate (a=2, b=2 to 12),polypropyleneglycol methacrylate (a=3, b=2 to 20),allyloxypolyethyleneglycol methacrylate, allyloxypolyethyleneglycolacrylate, stearoxypolyethyleneglycol methacrylate,stearoxypolyethyleneglycol acrylate,octoxypolyethyleneglycol-polypropyleneglycol acrylate (a=2.4, b=14, thenumber of ethylene groups in one molecule: 8, the number of propylenegroups in one molecule: 6), octoxypolyethyleneglycol-polypropyleneglycolmethacrylate (a=2.4, b=14, the number of ethylene groups in onemolecule: 8, the number of propylene groups in one molecule: 6),poly(propyleneglycol-tetramethyleneglycol)acrylate,poly(propyleneglycol-tetrarethyleneglycol)methacrylate,poly(ethyleneglycol-tetramethyleneglycol)acrylate,poly(ethyleneglycol-tetramethyleneglycol)methacrylate,poly(ethyleneglycol-propyleneglycol)acrylate,poly(ethyleneglycol-propyleneglycol)methacrylate, polypropyleneglycolacrylate and methoxypolyethyleneglycol methacrylate.

The compound represented by the formula (6) which is favorable for thefirst invention in the present application may include ethylene oxidemodified neopentylglycol dimethacrylate (R⁷=methyl; d=f=2; e=g=aninteger of 1 or more; R⁸=C₅H₁₀) and propylene oxide modified neopentylglycol diacrylate (R⁷=a hydrogen atom; d=f=3; e=g=an integer of 1 ormore; R⁸=C₅H₁₀)

The compound represented by the formula (7) which is favorable for thefirst invention in the present application may includetris(acryloxyethyl) isocyanurate (R⁹, R₁₀ and R¹¹ are allCH₂CH₂OCOCH═CH₂) and tris(methacryloxyethyl)isocyanurate (R⁹, R¹⁰ andR¹¹ are all CH₂CH₂OCOC(CH₃)═CH₂).

The compound represented by the formula (8) which is favorable for thefirst invention in the present application may include epichlorohydrinmodified glycerol triacrylate (R¹² and R¹⁵ are hydrogen atoms, R¹³ is—OCH₂CH(OH)CH₂—, R¹⁴ and R¹⁶ are each —CH₂OCH₂CH(OH)CH₂—), ethyleneoxide modified glycerol triacrylate (R¹² and R¹⁵ are hydrogen atoms, R¹³is —(C₂H₄O)_(j1)—, R¹⁴ and R¹⁶ are each —CH₂(C₂H₄O)_(j1)—, where j1 isan integer of 1 or more), propylene oxide modified glycerol triacrylate(R¹² and R¹⁵ are hydrogen atoms, R¹³ is —(C₃H₆O)_(j1)—, R¹⁴ and R¹⁶ areeach —CH₂(C₃H₆O)_(j1)—, where j1 is an integer of 1 or more),caprolactone modified trimethylolpropane triacrylate (R¹² is a hydrogenatom, R¹³ is —(C₅H₁₂COO)_(j1)—, R¹⁴ and R¹⁶ are each —CH₂(C₃H₆O)_(j1)—,R¹⁵ is an ethyl group, where j1 is an integer of 1 or more), ethyleneoxide modified trimethylolpropane triacrylate (R¹² is a hydrogen atom,R¹³ is —(C₂H₄O)_(j2)—, R¹⁴ and R¹⁶ are each —CH₂(C₂H₄O)_(j2)—, R¹⁵ is anethyl group, where j2 is an integer), and propylene oxide modifiedtrimethylolpropane triacrylate (R¹² is a hydrogen atom, R¹³ is—(C₃H₆O)_(j2)—, R¹⁴ and R¹⁶ are each —CH₂(C₃H₆O)_(j2)—, R¹⁵ is an ethylgroup, where j2 is an integer).

In the compound of the formula (8) which is favorable for the firstinvention in the present application, a compound wherein R¹⁴ and R¹⁶ aremethylene groups —CH₂— may also include pentaerythritol triacrylate,trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, andpentaerythritol tetraacrylate.

Further, the compound represented by the formula (9) which is favorablefor the first invention in the present application may includedipentaerythritol hydroxypentaacrylate, (R¹⁷is a hydrogen atom, R¹⁸ is—CH₂OH, R¹⁹ is —CH₂OCOCH═CH), and ditrimetylrolpropane tetraacrylate,(R¹⁷ is a hydrogen atom, R¹⁸ and R¹⁹ are each an ethyl group).

Besides these, hydroxypivalic acid neopentylglycol diacrylate,isostearyl monoacrylate, isostearyl monomethacrylate, vinyl p-tert-butylbenzoate and methoxyethyl methacrylate are also favorable as the firstresin precursor in the first invention in the present application.

Incidentally, of these first resin precursors, only a single compoundmay be used, or two or more compounds may as well be used incombination.

In order to materialize the high dispersion and low refractive index inthe resin precursor obtained by mixing the first and second resinprecursors, and the cured product thereof, the second resin precursormust have high dispersion (n_(F)−n_(C)>0.010) and also low refractiveindex (nd<1.62). This second resin precursor, in order to materializethe high dispersion without making the refractive index high as far aspossible, may preferably not contain the factor that makes therefractive index high, such as a sulfur molecule or a halogen atom.Also, in order to materialize the high dispersion, it may preferablycontain a ring structure such as a benzene ring in the molecule. Thering structure may be a ring consisting of only a single bond (σ-bond),but may preferably be a ring having a π-bond as in a benzene ringbecause much higher dispersion characteristics can be obtained. Like thefirst resin precursor, this second resin precursor may also preferablyhave a polymerizable functional group such as an acrylic group or amethacrylic group or a vinyl group in the molecule, in order tomaterialize the property of being polymerizable by light, heat or thelike.

As such a second resin precursor, a compound may be used which isrepresented by the following compositional formula (2) and has at leastone polymerizable functional group in the molecule and at least onebenzene ring in the molecule.C_(s1)H_(t1)O_(u1)N_(v1)  (2)wherein s1 and t1 are each an integer of 5 or more, and u1 and v1 areeach an integer of 0 or 1 or more and s1 or less.

This second resin precursor may include acrylate or methacrylate havinga bisphenol-A structure, other acrylate or methacrylate having a benzenering, and styrene. Stated specifically, it may preferably be a compoundrepresented by any of the following general formulas (10) to (12).

Here, R²⁰ and R²² are each a hydrogen atom or a methyl group, R²¹ andR²³ are each a divalent organic group, Z¹ is a divalent organic grouphaving at least one ring structure, Z² is a trivalent organic group, andh and i are each an integer. Incidentally, R²¹ and R²³ may preferablyconsists of C, H and O, Z¹ may preferably an organic group representedby any of the following general formulas (13) to (15), and Z² maypreferably an organic group represented by the following general formula(16).

Compounds favorable for the first invention in the present applicationas this second resin precursor may include, e.g., as the compoundrepresented by the formula (10), ethylene oxide modified bisphenol-Adiacrylate (R²⁰ is a hydrogen atom, R²¹ is —(OCH₂CH₂)_(k1)—, R²² is amethyl group, R²³ is —(OCH₂CH₂)_(k2)—, where k1 and k2 are integers),ethylene oxide modified bisphenol-A dimethacrylate (R²⁰ is a methylgroup, R²¹ is —(OCH₂CH₂)_(k1)—, R²² is a methyl group, R²³ is—(OCH₂CH₂)_(k2)—, where k1 and k2 are integers), propylene oxidemodified bisphenol-A diacrylate (R²⁰ is a hydrogen atom, R²¹ is—(OCH₂CH₂CH₂)_(k1)—, R²² is a methyl group, R²³ is —(OCH₂CH₂CH₂)_(k2)—,where k1 and k2 are integers), propylene oxide modified bisphenol-Adimethacrylate (R²⁰ and R²² are methyl groups, R²¹ is—(OCH₂CH₂CH₂)_(k1)—, R²³ is —(OCH₂CH₂CH₂)_(k2)—, where k1 and k2 areintegers), ethylene oxide modified hisphenol-F diacrylate (R²⁰ and R²²are hydrogen atoms, R²¹ is —(OCH₂CH₂)_(k1)—, R²³ is —(OCH₂CH₂)_(k2)—,where k1 and k2 are integers), ethylene oxide modified bisphenol-Fdimethacrylate (R²⁰ is a methyl group, R²¹ is —(OCH₂CH₂)_(k1)—, R²² is ahydrogen atom, R²³ is —(OCH₂CH₂)_(k2)—, where k1 and k2 are integers),propylene oxide modified bisphenol-F diacrylate (R²⁰ and R²² arehydrogen atoms, R²¹ is —(OCH₂CH₂CH₂)_(k1)—, R²³ is —(OCH₂CH₂CH₂)_(k2)—,where k1 and k2 are integers), propylene oxide modified bisphenol-Adiacrylate (R²⁰ is a hydrogen atom, R²¹ is —(OCH₂CH₂CH₂)_(k1)—, R²² is ahydrogen atom, R²³ is —(OCH₂CH₂CH₂)_(k2)—, where k1 and k2 areintegers), ethylene oxide-propylene oxide modified bisphenol-Adiacrylate (R²⁰ is a hydrogen atom, R²¹ is—(OCH₂CH₂)_(k1)—(OCH₂CH₂CH₂)_(k2)—, R²² is a methyl group, R²³ is—(OCH₂CH₂)_(k3)—(OCH₂CH₂CH₂)_(k4)—, where k1 to k4 are integers), andethylene oxide-propylene oxide modified bisphenol-A dimethacrylate (R²⁰and R²² are methyl groups, R²¹ is —(OCH₂CH₂)_(k1)—(OCH₂CH₂CH₂)_(k2)—,R²³ is —(OCH₂CH₂)_(k3)—(OCH₂CH₂CH₂)_(k4), where k1 to k4 are integers).

The compound represented by the formula (11) which is favorable for thefirst invention in the present application may include

-   [5,5′-(9H-fluoren-9-ylidene)bis{(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)}]2-propenoate,    in which the Z¹ group is represented by the formula (13);-   [5,5′-{4-(1,1′-biphenyl)methylene}bis{(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)}]2-propenoate,    in which the Z¹ group is represented by the formula (14); and-   [(1-phenylethylidene}bis{(4,1-phenylenepoly(oxy-2,1-ethanediyl)}]2-propenoate,    in which the Z¹ group is represented by the formula (15).

As the compound represented by the formula (12), e.g.,1,1-bis(p-acryloyloxyethyloxyphenyl)-1-[p″-{1′-(p′-acryloyloxyethyloxy)phenyl-1′-methylethyl}phenyl]ethane,in which the Z² group is represented by the formula (16) is favorablefor the first invention in the present application.

Besides these, also favorable for the first invention in the presentapplication as the second resin precursor are2,2-bis[4-(methacryloxyethoxy)phenyl]propane,2,2-bis[4-(methacryloxydiethoxy)phenyl]propane,2,2-bis[4-(methacryloxypolyethoxy)phenyl]propane,2,2-bis[4-(acryloxydiethoxy)phenyl]propane, phnoxyethyl acrylate,phnoxydiethyleneglycol acrylate, phnoxypolyethyleneglycol acrylate,2-hydroxy-3-phenoxypropyl acrylate, and so forth.

Incidentally, of these second resin precursors, only a single compoundmay be used, or two or more compounds may as well be used incombination.

The resin precursor composition of the first invention in the presentapplication may appropriately contain, in addition to the first andsecond resin precursors described above, a fifth resin precursor, apolymerization initiator and so forth for the purpose of viscositymodification or the like. As a polymerization initiator favorable forthe resin precursor composition of the first invention in the presentapplication, it may include, e.g., photopolymerization initiators suchas benzophenone, hydroxybenzophenone methanesulfonate, o-benzoylmethylbenzoate, p-chlorobenzophenone, p-dimethylaminobenzophenone, benzoin,benzoin allyl ether, benzoin methyl ether, benzoin ethyl ether, benzoinisobutyl ether, benzoin propyl ether, acetophenone,diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, benzyl dimethylketal, 2-hydroxy-2-methylpropiophenone,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropiophenone,1-phenyl-1,2-propanedione-2-o-benzoyloxime; and thermal-polymerizationinitiators as exemplified by azo compounds such asazobisisobutyronitrile and dimethyl 2,2′-azobisisobutyrate, andperoxides such as benzoyl peroxide and di(t-butyl) peroxide.

In the first invention in the present application, it further providesan optic-purpose resin which is a cured product obtained by curing theabove resin precursor composition of the first invention in the presentapplication. The optic-purpose resin of the first invention in thepresent application may preferably have a post-curing d-line refractiveindex n_(d) of less than 1.55 and have a difference of more than 0.010which is found by subtracting a post-curing C-line refractive indexn_(C) from a post-curing F-line refractive index n_(F).

In the first invention in the present application, it further providesan optical element comprising a first member formed of thisoptic-purpose resin of the first invention in the present application.The optical element of the first invention in the present applicationmay be used as a lens, a diffraction grating or the like in stillcameras, video cameras, eyeglasses, telescopes, binoculars, microscopes,pick-up lenses for optical disk/optical magnetic disk reading, and soforth. Accordingly, in the first invention in the present application,it also provides an optical article having the optical element of thefirst invention in the present application.

Incidentally, the optic-purpose resin of the first invention in thepresent application may be used in, besides single lenses, compositeoptical elements such as resin cemented optical elements. In particular,it is suited for, as shown in FIG. 1( b), a close-contact double-layertype diffractive optical element 10 comprising a first member 11 formedof an optical material having low refractive index and high dispersionand a second member 12 formed of a glass or resin having high refractiveindex and low dispersion.

Accordingly in the first invention in the present application, itprovides an optical element comprising a first member formed of theoptic-purpose resin of the first invention in the present applicationand a second member joined to the first member in close contact. Here,as the second member, an optical material may be used in which itsd-line refractive index n_(d2) is larger than a d-line refractive indexn_(d1) of the first member, and its dispersion (that is, a differencefound by subtracting a C-line refractive index n_(C2) of the secondmember from an F-line refractive index n_(F2) of the second member) issmaller than a dispersion of the first member (that is, a differencefound by subtracting a C-line refractive index n_(C1) of the firstmember from an F-line refractive index n_(F1) of the first member),whereby an element having especially useful optical characteristics canbe obtained. Stated specifically, both the materials for the first andsecond members are made to have a large difference in refractive index.This makes the height of diffraction gratings small to make theirproduction easy, and besides enables reduction of the angle dependenceof diffraction efficiency. Making both the materials have a largedifference in dispersion also enables reduction of the wavelengthdependence of diffraction efficiency.

Incidentally, glass or resin may be used in this second member. It ispreferable to use a glass having a glass transition temperature Tg lowerthan 400° C. Here, the glass includes sol-gel glass, inorganic glass andorganic glass, which are transparent materials usually having arefractive index n_(d) of from 1.4 to 2.0 and an Abbe constant ofapproximately from 20 to 100. As compositional components constitutingthe inorganic glass, they may include, e.g., SiO₂, B₂O₃, P₂O₅, Na₂O,K₂O, CaO, BaO, MgO, ZnO, PbO, MnO, Al₂O₃, Fe₂O₃, Sb₂O₃, As₂O₃, TiO₂,La₂O₃, ZrO₂ and KHF₂. Also, the organic glass may include polyacrylate,polymethacrylate, polyvinyl chloride, polyesters, celluloid, andcellulose derivatives.

There are no particular limitations on methods for molding the secondmember. For example, usable are a method in which the shape of a mold istransferred when the material is cured, an injection molding technique,and so forth. Further, in the case when the glass is used in the secondmember, usable are shape production by grinding, a method in which ashape is transferred while carrying out grinding by means of a formgrinding wheel having a reverse lattice shape, and what is called glassmold technique, in which a shape is transferred by pressing a moldagainst a glass softened at a high temperature. Incidentally, in thecase when the glass mold technique is used, it is difficult to work aheat-resistant mold because in diffraction gratings the shape to betransferred is complicate compared with usual aspheric lenses. However,a low-melting glass having a low glass transition temperature Tg may beused, whereby the range of selection can be broadened in respect ofmolds that can be used.

As a first resin favorable for the second invention in the presentapplication, it may include alicyclic olefin resins, alicyclic acrylicresins, alicyclic polyurethane resins, resins having an episulfidestructure, and epoxy-acrylate resins having an alicyclic structure. Ofthese, a single resin may be used, or two or more types of resins may beused in the form of a mixture. Incidentally, it is preferable for thefirst resin to contain a sulfur atom in the repeating unit, becauseoptical characteristics can be more improved.

The alicyclic olefin resin favorable as the first resin may include acompound represented by the following general formula (17).

Here, R³¹ and R³² are each amonovalent or divalent organic group. In thecase when R³¹ and R³² are each a divalent organic group, these combinewith each other to form part of the cyclic structure Also, n is aninteger of 1 or more. The alicyclic olefin resin used in the secondinvention in the present application may preferably have a molecularweight of from 5,000 to 45,000.

In this alicyclic olefin resin of the formula (17), the properties ofthe resin change depending on the structure and combination of thesubstituents R³¹ and R³². Where R³¹ and R³² combine to constitute a ringstructure to form a bulky atomic group, the resin comes colorless andtransparent, and hence this is especially suited for the use in opticalelements. Such a resin in which R³¹ and R³² constitute a ring structuremay include a resin represented by any of the following structuralformulas (18). Incidentally, m is an integer of 0 or more.

The alicyclic olefin resin used in the second invention in the presentapplication may consist of only one type of any of these repeatingunits, or may be a copolymer consisting of two or more repeating units.

This alicyclic olefin resin may further have a polar group in themolecule as in the following general formula (19). This is preferablebecause the resin can have a high affinity for inorganic materials ormany polar organic materials and can be improved in formability.

Here, n is an integer of 1 or more. The alicyclic olefin resin used inthe second invention in the present application may preferably have amolecular weight of from 5,000 to 45,000. R³³ is a polar group such asan acyl group or an acyloxy group. R³⁴ is an organic group such as ahydrogen atom or an alkyl group. Combination of R³³ and R³⁴ may include,e.g., (R³³/R³⁴)═(CO₂CH₃/H), (CO₂CH₃/CH₃), (CO₂C₂H₅/CH₃) and the like.

The alicyclic acrylic resin is a resin having analicyclic structure inthe side chain of acrylic resin. The alicyclic acrylic resin favorablefor the first resin may include, e.g., a resin represented by thefollowing general formula (20).

Here, R³⁵ is a hydrogen atom or an alkyl group (e.g., a methyl group).Also, R³⁶ is a cyclic aliphatic group, which may preferably be, e.g., acycloalkyl group represented by any of the following structural formulas(21). Letter symbol p is an integer of 1 or more, and the alicyclicacrylic resin used in the second invention in the present applicationmay preferably have a molecular weight of from 5,000 to 45,000.

These cyclic aliphatic groups may also each further have a substituentas shown in the following structural formula (22).

The alicyclic olefin resin used in the second invention in the presentapplication may have as R³⁶ only any one type of these cyclic aliphaticgroups, or may be a copolymer having two or more of these in themolecule. It may also be a copolymer further having in the molecule, inaddition to the repeating unit represented by the formula (20), at leastone of repeating units represented by the following formula (23). Here,R³⁷ is an ethyl group or a methyl group.

The alicyclic polyurethane resin favorable for the first resin mayinclude, e.g., a polyurethane formed by the reaction of a diisocyanatecompound having a cyclic structure with a polyol compound or a polythiolcompound.

The diisocyanate compound having a cyclic structure may include adiisocyanate compound represented by the following general formula (24),isophorone diisocyanate, methylenebis(4-cyclohexylisocyanate), andhydrogenated xylilene diisocyanate. Any of these may be used alone, ormay be used in combination of two or more types.

Here, R³⁸ and R³⁹ are each a hydrogen atom or a methyl group. Such adiisocyanate compound may include 4,4-dicyclohexylmethane diisocyanateand 4,4-isopropylidenebis(4-cyclohexylisocyanate).

Meanwhile, the polyol compound favorable for the second invention in thepresent application may include ethyleneglycol, propyleneglycol,neopentyl glycol, diethyleneglycol, dipropyleneglycol, hydrogenatedbisphenol-A, 2,2′-di(4-hydroxypropoxyphenyl)propane, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethyleneglycol,triethyleneglycol, and pentaerythritol diallyl ether. Also, thepolythiol compound favorable for the second invention in the presentapplication may include 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropanerepresented by the following structural formula (25).

These polyols and polythiol, any one type may be used alone, or two ormore types may be used in combination. Incidentally, the more thepolythiol is used, the higher the refractive index tends to be. Hence,such use is preferable.

The alicyclic poly urethane resin favorable for the first resin may alsobe a urethane acrylate or methacrylate made into acrylate ormethacrylate by the reaction with an acrylate or methacrylate having ahydroxyl group. The acrylate or methacrylate having a hydroxyl group mayinclude, e.g., 2-hydroxyethyl acrylate or methacrylate, hydroxypropylacrylate or methacrylate, polyethyleneglycol acrylate or methacrylate,polypropyleneglycol monoacrylate or monomethacrylate, glycerolmonoacrylate, and glycerol diacrylate.

The resin having an episulfide structure favorable for the first resinis an organic high-molecular compound having in the molecule at leastone atomic group represented by the following structural formula (26).

Here, R⁴⁰ represents a hydrocarbon group having 1 to 10 carbon atoms;and R⁴¹, R⁴² and R⁴³ each represent a hydrogen atom or a hydrocarbongroup having 1 to 10 carbon atoms. X represents a sulfur atom or anoxygen atom. The number of sulfur atoms held in the total number of Xgroups contained in one molecule may preferably be 50% or more on theaverage.

This atomic group represented by the structural formula (26) maypreferably be present in a number of two or more in the molecule. Ascompounds having a chainlike aliphatic skeleton in which this atomicgroup has combined in a number of two or more, favorable for the secondinvention in the present application are, e.g.,bis(β-epithiopropylthio)methane, 1,2-bis(β-epithiopropylthio)ethane,1,3-bis(β-epithiopropylthio)propane,1,2-bis(β-epithiopropylthio)propane,1-(β-epithiopropylthic)-2-(β-epithiopropylthiomethyl)pro pane,1,4-bis(β-epithiopropylthio)butane, 1,3-bis(β-epithiopropylthio)butane,1-(β-epithiopropylthio)-3-(β-epithiopropylthiomethyl)butane,1,5-bis(β-epithiopropylthio)pentane,1-(β-epithiopropylthio)-4-(β-epithiopropylthiomethyl)pentane,1,6-bis(β-epithiopropylthio)hexane,1-(β-epithiopropylthio)-5-(β-epithiopropylthiomethyl)hexane,1-(β-epithiopropylthio)-2-[(2-β-epithiopropylthioethyl)thio] ethane, and1-(β-epithiopropylthio)-2-[{2-(2-β-epithiopropylthioethyl)thioethyl}thio]ethane.Compounds wherein at least one hydrogen atom of the episulfide group ofany of these compounds has been substituted with a methyl group may alsobe included as compounds favorable for the second invention in thepresent application.

Further, as compounds having a cyclic aliphatic skeleton in which theatomic group represented by the structural formula (26) has combined ina number of two or more, favorable for the second invention in thepresent application are, e.g., cyclic aliphatic organic compounds suchas 1,3-bis(β-epithiopropylthio)cyclohexane,1,4-bis(β-epithiopropylthio)cyclohexane,1,3-bis(β-epithiopropylthiomethyl)cyclohexane,1,4-bis(β-epithiopropylthiomethyl)cyclohexane,bis[4-(β-epithiopropylthio)cyclohexyl]methane,2,2-bis[4-(β-epithiopropylthio)cyclohexyl]propane,bis[4-(β-epithiopropylthio)cyclohexyl]sulfide,2,5-bis(β-epithiopropylthiomethyl)-1,4-dithian, and2,5-bis(β-epithiopropylthioethylthiomethyl)-1,4-dithian. Compoundswherein at least one hydrogen atom of the episulfide group of any ofthese compounds has been substituted with a methyl group may also beincluded as compounds favorable for the second invention in the presentapplication.

The epoxy-acrylate resin having an alicyclic structure favorable as thefirst resin may include epoxy-acrylate resins having an alicyclicstructure as exemplified by:

a cycloalkyl structure such as cyclopentane, cyclohexane or cyclooctane;

a hydrogenated cyclic structure formed by hydrogenation of(hydrogenating) an aromatic ring such as benzene, naphthalene,anthracene, pentalene, indene, azulene, heptalene, biphenylene,indacene, acenaphthylene, fluorene, phenanthrene, fluoranthene,acephenanthrylene, aceanthrylene, triphenylene, chrysene, pyrene,naphthacene, picene, perylene, pentaphene, pentacene, bisphenol A,bisphenol F, bisphenol S or phenol novolak resin;

a polycyclic structure such as tricyclodecane, bicycloheptane,norbornane, diocyclopentane, pinane or bornane;

a spiro structure such as spiro[3.4]octane or2,4,8,10-tetraoxaspiro[5.5]undecane;

a heterocyclic structure such as oxorane, thiorane, silorane, dioxane orthioisatiane; and

a hydrogenated heterocyclic structure such as thiazole, oxathiazine,dithiazien, furan, thiophene, pyrrole, oxazole, imidazole, pyran,pyridine, pyrroline, piperidine, piperadine, morpholine, indole,quinoline, xanthene, carbazole, acridine, indolineand coumarone. Inparticular, those containing a phenolic hydroxyl group in startingmaterials are preferred because they afford a good yield and improve thepurity of epoxy-acrylate.

Incidentally, in the case when the epoxy-acrylate resin havinganalicyclic structure is synthesized from the compound having a saturatedcyclic structure, the compound having a saturated cyclic structure maybe made into glycidyl ether using epichlorohydrin or glycidol, which isthen allowed to react with a compound having a polymerizable unsaturatedgroup and a carboxyl group at a terminal, such as acrylic acid ormethacrylic acid, to synthesize a compound as represented by thefollowing structural formula (27), and this may be polymerized. Here, inthe formula (27), R⁴⁴ is a divalent organic group (preferably ahydrocarbon group).

In the case when the substance having a phenolic hydroxyl group is usedas a starting material, the starting material may be made into glycidylether using epichlorohydrin, which is thereafter hydrogenated to have asaturated cyclic structure, and this is allowed to react with a compoundhaving a polymerizable unsaturated group and a carboxyl group at aterminal, such as acrylic acid or methacrylic acid, to synthesize acompound as represented by the following structural formula (28), andthis maybe polymerized. Here, q is an integer of 1 or more.

The second resin may preferably not contain any of a sulfur atom, achlorine atom, a bromine atom and an iodine atom in the molecule. Thesecond resin may also preferably be an ultraviolet-curable resin becauseit may be formed without heating at a high temperature.

As examples of a resin containing fluorine, favorable as the secondresin used in the second invention in the present application, it mayinclude 2,2,2-trifluoroethyl methacrylate, 2,2,2-trifluoroethylacrylate, β-(perfluoroethyl)ethyl methacrylate, β-(perfluoroethyl)ethylacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate,1,1,1,3,3,3-hexafluoroisopropyl acrylate, 2,2,2-trifluoroethylmethacrylate, 2,2,2-trifluoroethyl acrylate, 2,2,3,3-tetrafluoropropylmethacrylate, 2,2,3,3-tetrafluoropropyl methacrylate,2,2,3,4,4,4-hexafluorobutyl methacrylate, 2,2,3,4,4,4-hexafluorobutylmethacrylate, octafluoropentyl methacrylate and octafluoropentylacrylate.

As examples of a resin containing a benzene ring, favorable as thesecond resin used in the second invention in the present application, itmay include a compound represented by any of the following generalformulas (29) to (31), and those obtained by polymerizing2-hydroxy-3-phenoxypropyl acrylate or methacrylate, phenoxyethylacrylate or methacrylate, phenoxydiethyleneglycol acrylate ormethacrylate, benzyl acrylate or methacrylate,p-cumylphenoxyethyleneglycol acrylate or methacrylate or the like.

CH₂═CHCO—(OCH₂CH₂)_(r)—O-Z-O—(CH₂CH₂O)_(t)—COCH═CH₂  (30)

In the formula (29), R⁴⁵ and R⁴⁶ are each a hydrogen atom, a methylgroup or a trifluoromethyl group, R⁴⁷ and R⁴⁸ are each—(OCH₂CH₂)_(a)—(OCH₂CH₂CH₂)_(b)—. Herer, a and b are each an integer of0 or 1 or more.

This compound represented by the formula (29) may include, e.g.;

EO modified bisphenol-A diacrylate (R⁴⁵ is a hydrogen atom, R⁴⁶ is amethyl group, R⁴⁷ is —(OCH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂)_(g1)—, where f1and g1 are each an integer of 1 or more and may preferably be 30 orless);

EO modified bisphenol-A dimethacrylate (R⁴⁵ is a methyl group, R⁴⁶ is amethyl group, R⁴⁷ is —(OCH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂)_(g1)—, where f1and g1 are each an integer of 1 or more and may preferably be 30 orless);

PO modified bisphenol-A diacrylate (R⁴⁵ is a hydrogen atom, R⁴⁶ is amethyl group, R⁴⁷ is —(OCH₂CH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂CH₂)_(g1)—,where f1 and g1 are each an integer of 1 or more and may preferably be30 or less);

PO modified bisphenol-A dimethacrylate (R⁴⁵ is a methyl group, R⁴⁶ is amethyl group, R⁴⁷ is —(OCH₂CH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂CH₂)_(g1)—,where f1 and g1 are each an integer of 1 or more and may preferably be30 or less);

EO modified bisphenol-F diacrylate (R⁴⁵ is a hydrogen atom, R⁴⁶ is is—CF3, R⁴⁷ is —(OCH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂)_(g1)—, where f1 and g1are each an integer of 1 or more and may preferably be 30 or less);

EO modified bisphenol-F dimethacrylate (R⁴⁵ is a methyl group, R⁴⁶ is ahydrogen atom, R⁴⁷ is —(OCH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂)_(g1)—, wheref1 and g1 are each an integer of 1 or more and may preferably be 30 orless);

PO modified bisphenol-F diacrylate (R⁴⁵ is a hydrogen atom, R⁴⁶ is ahydrogen atom, R⁴⁷ is —(OCH₂CH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂CH₂)_(g1)—,where f1 and g1 are each an integer of 1 or more and may preferably be30 or less);

PO modified bisphenol-F diacrylate (R⁴⁵ is amethyl group, R⁴⁶ is ahydrogen atom, R⁴⁷ is —(OCH₂CH₂CH₂)_(f1)—, R⁴⁸ is —(OCH₂CH₂CH₂)_(g1)—,where f1 and g1 are each an integer of 1 or more and may preferably be30 or less);

EO, PO modified bisphenol-A acrylate (R⁴⁵ is a hydrogen atom, R⁴⁶ is amethyl group, R⁴⁷ is —(OC₂H₄)_(f1)—(OC₃H₆)_(g1)—, R⁴⁸ is—(OC₂H₄)_(h1)—(OC₃H₆)_(i1)—, where f1, g1, h1 and i1 are each an integerof 1 or more and may preferably be 30 or less); and

EO, PO modified bisphenol-A methacrylate (R⁴⁵ is a methyl group, R⁴⁶ isa methyl group, R⁴⁷ is —(OC₂H₄)_(f1)—(OC₃H₆)_(g1)—, R⁴⁸ is—(OC₂H₄)_(h1)—(OC₃H₆)_(i1)—, where f1, g1, h1 and i1 are each an integerof 1 or more and may preferably be 30 or less).

In the formula (30), Z is a divalent group represented by any of thefollowing structural formulas (32), and r and t are each an integer of 1or more and may preferably be 10 or less.

This compound represented by the formula (30) may include, e.g.,2-propenic acid5,5′-[9H-fluoren-9-ylidene]bis[(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)]ester,2-propenic acid5,5′-[4-(1,1′-biphenyl)methylene]bis[(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)]ester, and 2-propenic acid[(1-phenylethylidene)bis[(4,1-phenylenepoly(oxy-2,1-ethanediyl)]ester.

The compound represented by the formula (31) may also include 2-propenicacid 1-[4-{1-(4-phenyleneoxyethyl)-1-methylethyl}phenyl]ethylidenebis(4-phenyleneoxyethyl)ester.

As examples of a resin containing both a fluorine atom and a benzenering, favorable as the second resin used in the second invention in thepresent application, it may include resins obtained by allowing a diolrepresented by any of the following structural formulas (33) to reactwith acrylate or methacrylate. These resins may be subjected to ethyleneoxide (i.e., EO) modification or propylene oxide (i.e., PO)modification.

Of these compounds favorable as the second resin, only one type may beused, or two or more types may also be used in combination. A copolymerof any of these may also be used.

In the second invention in the present application, it is preferablethat the second member has a d-line refractive index n_(d1) of 1.45 ormore and the second member has an average dispersion MD₁ of 0.02 orless. It is also preferable that the first member has a d-linerefractive index n_(d2) of 1.60 or less and the first member has anaverage dispersion MD₂ of 0.01 or more.

Accordingly, the present invention provides an optical material having ad-line refractive index n_(d) of 1.60 or less and an average dispersionMD of 0.01 or more; the d-line refractive index n_(d) and the averagedispersion MD being in the relationship of:n _(d)≦8.8×MD+1.402; andcomprising organic matter only, and provides an optical elementcomprising the first member comprising the optical material.

It is further preferable that a difference found by subtracting thed-line refractive index n_(d2) of the first member from the d-linerefractive index n_(d1) of the second member is 0.03 or more and adifference found by subtracting the average dispersion MD₂ of the firstmember from the average dispersion MD₁ of the second member is −0.003 orless.

Thus, resins having a large difference in refractive index are used inthe first and second members. This makes the height of diffractiongratings small to make their production easy, and besides enablesreduction of the angle dependence of diffraction efficiency. Also,resins having a large difference in average dispersion are used in thefirst and second members. This enables reduction of the wavelengthdependence of diffraction efficiency.

There are no particular limitations on methods for molding the first andsecond members. For example, usable are a method in which the shape of amold is transferred when the material is cured, an injection moldingtechnique, and so forth. Also, as methods for the curing, the materialmay be cured by heating, or by leaving to cool, depending on the typesof resins used, or may be cured by exposure. Of the first member and thesecond member, in respect of the member to be formed later, the materialmay preferably be cured by exposure using an ultraviolet-curable resin,which can be cured without heating, in order that the member havingalready been molded can be prevented from its deformation and change ofproperties.

In the second invention in the present application, both the firstmember and the second member are formed of the resin, and hence theresin can well be put full in grooves of molds because it is molded in auncured or softened low-viscosity state, so that good transfer can beachieved. It may also be molded at a temperature lower than the glass,and hence materials for molds can be selected in a wide range. Hence,according to the second invention in the present application, ahigh-precision close-contact double-layer type diffractive opticalelement can be produced at a low cost. Incidentally, there are noparticular limitations on materials for the base material, which may aswell be resin or glass.

The optical element of the second invention in the present applicationmay be used in optical systems such as still cameras, video cameras,telescopes, binoculars and microscopes, and in pick-up lenses foroptical disk/optical magnetic disk reading. Accordingly, in the secondinvention in the present application, it also provides an opticalarticle having the optical element of the second invention in thepresent application.

EXAMPLES Example 1

A. Preparation of Resin Precursor Composition

(1) Resin Precursor Composition I

Using as a first resin precursor 2,2,2-trifluoroethyl methacrylate(n_(d)=1.3605, n_(F)−n_(C)=0.0075), a compound represented by theformula (3), and using as a second resin precurs or ethylene oxidemodified bisphenol-A dimethacrylate (n_(d)=1.5425, n_(F)−n_(C)=0.0164),a compound represented by the formula (10) where R²⁰ and R²² are methylgroups, R²¹ is —(OCH₂CH₂)_(w1)—, R²³ is —(OCH₂CH₂)_(w2)—, and w1+w2=2.2,the first resin precursor and the second resin precursor were mixed in avolume ratio of 1:9, and thoroughly stirred to prepare Resin PrecursorComposition I. Resin Precursor Composition I obtained had opticalconstants of a refractive index n_(d) of 1.5243 and a dispersion(n_(F)−n_(C)) of 0.0155.

(2) Resin Precursor Composition II

Using as a first resin precursor 1,3-butyleneglycol diacrylate(n_(d)=1.4500, n_(F)−n_(C)=0.0093), a compound represented by theformula (4), and using as a second resin precursor ethylene oxidemodified bisphenol-A dimethacrylate (n_(d)=1.5322, n_(F)−n_(C)=0.0152) acompound represented by the formula (10) where R²⁰ and R²² are methylgroups, R²¹ is —(OCH₂CH₂)_(w1)—, R²³ is —(OCH₂CH₂)_(w2)—, and w1+w2=4,the first resin precursor and the second resin precursor were mixed in avolume ratio of 3:7, and thoroughly stirred to prepare Resin PrecursorComposition II. Resin Precursor Composition I: obtained had opticalconstants of a refractive index n_(d) of 1.5075 and a dispersion(n_(F)−n_(C)) of 0.0134.

(3) Resin Precursor Composition III

Using as a first resin precursor dimethylaminoethyl methacrylate(n_(d)=1.4391, n_(F)−n_(C)=0.0093), a compound represented by theformula (5), and using as a second resin precursor[5,5′-(9H-fluoren-9-ylidene)bis{(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)}]2-propenoate(n_(d)=1.610, n_(F)−n_(C)=0.0169), a compound represented by the formula(11), the first resin precursor and the second resin precursor weremixed in a volume ratio of 5:5, and thoroughly stirred to prepare ResinPrecursor Composition III. Resin Precursor Composition III obtained hadoptical constants of a refractive index n_(d) of 1.5245 and a dispersion(n_(F)−n_(C)) of 0.0131.

(4) Resin Precursor Composition IV

Using as a first resin precursor propylene oxide modified neopentylglycol diacrylate (n_(d)=1.446, n_(F)−n_(C)=0.0098), a compoundrepresented by the formula (6) where R⁷ is a hydrogen atom, R⁸ is—C₅H₁₀—, d and f are 3, and e and g are 1, and using as a second resinprecursor ethylene oxide modified bisphenol-A dimethacrylate(n_(d)=1.5425, n_(F)−n_(C)=0.0164), a compound represented by theformula (10) where R²⁰ and R²² are methyl groups, R²¹ is—(OCH₂CH₂)_(w1)—, R²³ is —(OCH₂CH₂)_(w2)—, and w1+w2=2.2, the firstresin precursor and the second resin precursor were mixed in a volumeratio of 5:5, and thoroughly stirred to prepare Resin PrecursorComposition IV. Resin Precursor Composition IV obtained had opticalconstants of a refractive index n_(d) of 1.4943 and a dispersion(n_(F)−n_(C)) of 0.0131.

(5) Resin Precursor Composition V

Using as a first resin precursor tris(acryloxyethyl)isocyanurate(n_(d)=1.4520, n_(F)−n_(C)=0.0092), a compound represented by theformula (7) where R⁹ to R₁₁ are all CH₂CH₂OCOCH═CH₂, and using as asecond resin precursor ethylene oxide modified bisphenol-Adimethacrylate (n_(d)=1.5322, n_(F)−n_(C)=0.0152), a compoundrepresented by the formula (10) where R²⁰ and R²² are methyl groups, R²¹is —(OCH₂CH₂)_(w1)—, R²³ is —(OCH₂CH₂)_(w2)—, and w1+w2=4, the firstresin precursor and the second resin precursor were mixed in a volumeratio of 4:6, and thoroughly stirred to prepare Resin PrecursorComposition V. Resin Precursor Composition V obtained had opticalconstants of a refractive index n_(d) of 1.5001 and a dispersion(n_(F)−n_(C)) of 0.0128.

(6) Resin Precursor Composition VI

Using as a first resin precursor ethylene oxide modified glyceroltriacrylate (n_(d)=1.4750, n_(F)−n_(C)=0.0086), a compound representedby the formula (8) where R¹² and R¹⁵ are hydrogen atoms, and R¹³, R¹⁴and R¹⁶ are each —C₅H₁₀, and using as a second resin precursor ethyleneoxide modified bisphenol-A dimethacrylate (n_(d)=1.5322,n_(F)−n_(C)=0.0152), a compound represented by the formula (10) whereR²⁰ and R²² are methyl groups; R²¹ is —(OCH₂CH₂)_(w1)—, R²³ is—(OCH₂CH₂)_(w2)—, and w1+w2=4, the first resin precursor and the secondresin precursor were mixed in a volume ratio of 5:5, and thoroughlystirred to prepare Resin Precursor Composition VI. Resin PrecursorComposition VI obtained had optical constants of a refractive indexn_(d) of 1.5036 and a dispersion (n_(F)−n_(C)) of 0.0119.

(7) Resin Precursor Composition VII

Using as a first resin precursor pentaerythritol triacrylate(n_(d)=1.4822, n_(F)−n_(C)=0.0093), a compound represented by theformula (9), and using as a second resin precursor ethylene oxidemodified bisphenol-A dimethacrylate (n_(d)=1.5425, n_(F)−n_(C)=0.0164),a compound represented by the formula (10) where R²⁰ and R²² are methylgroups, R²¹ is —(OCH₂CH₂)_(w1)—, R²³ is —(OCH₂CH_(w2))_(w2)—, andw1+w2=2.2, the first resin precursor and the second resin precursor weremixed in a volume ratio of 7:3, and thoroughly stirred to prepare ResinPrecursor Composition VII. Resin Precursor Composition VII obtained hadoptical constants of a refractive index n_(d) of 1.5003 and a dispersion(n_(F)−n_(C)) of 0.0114.

(8) Resin Precursor Composition VIII

Using as a first resin precursor dipentaerythritol hydroxypentaacrylate(n_(d)=1.4855, n_(F)−n_(C)=0.0089), a compound represented by theformula (9), and using as a second resin precursor ethylene oxidemodified bisphenol-A dimethacrylate (n_(d)=1.5425, n_(F)−n_(C)=0.0164),a compound represented by the formula (10) where R²⁰ and R²² are methylgroups, R²¹ is —(OCH₂CH₂)_(w1)—, R²³ is —(OCH₂CH₂)_(w2)—, and w1+w2=2.2,the first resin precursor and the second resin precursor were mixed in avolume ratio of 7:3, and thoroughly stirred to prepare Resin PrecursorComposition VIII. Resin Precursor Composition VIII obtained had opticalconstants of a refractive index n_(d) of 1.5026 and a dispersion(n_(F)−n_(C)) of 0.0112.

(9) Resin Precursor Composition IX

Using as a first resin precursor 2,2,2-trifluoroethyl methacrylate(n_(d)=1.36.5, n_(F)−n_(C)=0.0075), a compound represented by theformula (9), and using as a second resin precursor1,1-bis(p-acryloyloxyethyloxyphenyl)-1-[p″-{1′-(p′-acryloyloxyethyloxy)phenyl-1′-methylethyl}phenyl]ethane,the first resin precursor and the second resin precursor were mixed in avolume ratio of 3:7, and thoroughly stirred to prepare Resin PrecursorComposition IX. Resin Precursor Composition IX obtained had opticalconstants of a refractive index n_(d) of 1.5121 and a dispersion(n_(F)−n_(C)) of 0.0143.

B. Preparation of Optic-purpose Resin

(1) Photosetting Resin

In Resin Precursor Compositions I to V, 1% by weight each of1-hydroxycyclohexyl phenyl ketone was dissolved as a photopolymerizationinitiator, and these were thoroughly stirred. Next, the resultant resinprecursor compositions were casted into a matrix made by putting glasssheets together, followed by irradiation with ultraviolet rays of ahigh-pressure mercury lamp for 2 minutes optical constants of thetransparent cured products thus obtained were measured to obtain theresults shown in Table 1.

TABLE 1 Resin Precursor Gel percentage Composition n_(d) n_(F)–n_(c) (%)I 1.5440 0.0153 97 II 1.5285 0.0131 98 III 1.5451 0.0127 98 IV 1.51330.0128 97 V 1.5251 0.0125 97

Incidentally, the gel percentage was determined in the following way.First, about 0.5 g of the resin cured product was dried in a desiccatorfor about a day, and thereafter its mass (represented by a) wasprecisely measured. Next, the resin having been dried was immersed in70° C. methyl ethyl ketone for about 6 hours while changing the methylethyl ketone for new one at intervals of 2 hours, and thereafter thiswas left in the desiccator for a day. Subsequently, the resin was driedat 100° C. for 2 hours, and then further left in the desiccator for 1hour to cool to room temperature. Thereafter, its mass (represented byb) was precisely measured, and the gel percentage was calculatedaccording to:Gel percentage=(b/a)×100(%).

It is considered that the deterioration of weather ability of resins iscaused by unreacted functional groups remaining also after molding,which cause various side reactions such as coloring of resins over along period of time. Resins having a higher gel percentage areconsidered to have fewer unreacted functional groups, and hence havesuperior weatherability. In fact, weatherability having no problem inpractical use is achievable in resins having a gel percentage of 95% ormore. In those having a gel percentage of 96% or more, especiallysuperior weatherability is achievable.

(2) Thermosetting Resin

In Resin Precursor Compositions VI to IX, 0.3% by weight each ofazobisisobutylonitrile was dissolved as a thermal-polymerizationinitiator, and these were thoroughly stirred. Next, the resultant resinprecursor compositions were casted into the same matrix as that in theabove case of photosetting, and thereafter put into an oven, where thetemperature was raised from room temperature to 60° C. over a period of5 hours, thereafter raised to 80° C. over a period of 3 hours, andfurther raised to 100° C. over a period of 2 hours. At 100° C., thecompositions were further heated for 1 hour, followed by cooling, andthen mold release to obtain colorless transparent cured products.Optical constants of the transparent cured products thus obtained weremeasured to obtain the results shown in Table 2.

TABLE 2 Resin Precursor Gel percentage Composition n_(d) n_(F)–n_(c) (%)VI 1.5286 0.0115 98 VII 1.5219 0.0111 98 VIII 1.5263 0.0110 98 IX 1.53410.0141 98

C. Production of Optical Element

(1) Molding of Second Member

Molding low-melting glass P-SK60 (n_(d)=1.59087, n_(F)−n_(C)=0.00948),available from SUMITA optical Glass, Inc., was molded by glass moldingto transfer a lattice shape to the surface to produce a second member 12shown in FIG. 1( a) Incidentally, the molding was carried out at atemperature of 440° C., keeping the atmosphere in vacuum during heating.Also, a mold was produced using a mold base made of stainless steel onwhich Ni—P plating was applied, where the plating layer formed wasworked by cutting to form a shape reverse to that shown in FIG. 1. As acutting tool, a cutting tool whose tip curvature was 2 μm was used. Inthe second member shown in FIG. 1( a), it was in an outer diameter of 60mm, a lattice height of 12.5 μm, and a lattice pitch of about 2 mm atthe center and its vicinity and about 120 μm on the periphery, settingpitches smaller as lattices come up to the periphery.

(2) Molding of First Member

To the first resin precursor composition, 1% by weight each of1-hydroxycyclohexyl phenyl ketone was added as a photopolymerizationinitiator, and these were thoroughly stirred. The resin precursorcomposition obtained was dropped to the lattice-molded surface of theabove second member 12 with lattices formed by molding, and then a moldwas put close thereto from above to make the resin held full between themold and the glass. Next, this was irradiated with ultraviolet rays by ahigh-pressure mercury lamp on the side of the second member, andthereafter the mold was released to shape the first member. Thus, acomposite optical element 10 shown in FIG. 1( b) was produced, having alattice shape at its joint.

Example 2

First, a cyclic olefin resin (ZEONEX, available from Nippon Zeon Co.,Ltd.) having a repeating unit represented by the following structuralformula (34) was injection-molded to form a second member 12 shown inFIG. 2( a). Incidentally, in carrying out the molding, the cylindertemperature was set to 210° C., and the mold temperature to 100° C.

Subsequently, 58% by weight of 2,2,2-trifluoroethyl ethacrylaterepresented by the following structural formula (35), 41.5% by weight of2-propenic acid5,5′-(9H-fluoren-9-ylidene)bis[(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)]esterrepresented by the following structural formula (36) and 0.5% by weightof a photopolymerization initiator (IRGACURE 184, available from CibaSpeciality Chemicals Co.) were mixed to prepare an ultraviolet-curableresin composition.CH₂═C(CH₃)COOCH₂CF₃  (35)

(wherein x is an integer of 1 or more).

This ultraviolet-curable resin composition was dropped to thelattice-molded surface of the above second member 12, and then a moldwas put close thereto from above to make the resin held full between themold and the second member. Thereafter, this was irradiated withultraviolet rays by a high-pressure mercury lamp on the side of thesecond member 12 to effect curing, and the mold was released. Thus, afirst member 11 shown in FIG. 2( b) was formed.

In this way, a close-contact double-layer type diffractive opticalelement 10 was obtained. Incidentally, the element obtained was in anouter diameter of 60 mm, a lattice height of 20 μm, and a lattice pitchof about 2 mm at the center and its vicinity and about 120 μm on theperiphery, setting pitches smaller as lattices came up to the periphery.The diffractive optical element 10 obtained according to this Examplehad the stated optical characteristics in a good precision. This wasused in an optical system to manufacture a camera. As a result, thecamera obtained was able to photograph to obtain good images that arefree of blur because of the correction of chromatic aberration by theuse of this diffractive optical element.

The refractive indexes n_(d1) and n_(d2) average dispersions MD₁ and MD₂and their differences n_(d1)−n_(d2) and MD₁-MD₂ of the resin used ineach lattice member in this Example are each shown in Table 3.

TABLE 3 n_(d) MD Example 2 First member 1.500 0.0129 Second member 1.5300.0098 Difference 0.030 0.0031 Example 3 First member 1.545 0.0172Second member 1.594 0.0142 Difference 0.050 0.0030

Example 3

First, 0.3 mol of dicylclohexylmethane-4,4′-doisocyanate, 0.2 mol of1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane and 0.3% by weight(based on the whole resin) of dibutyltin dilaurate were so mixed as tocome uniform to prepare a cyclic thiourethane resin.

The cylic thiourethane resin obtained was made held full between a basematerial 23 formed of an optical glass and a mold having a moldingsurface and coated with a release agent on the molding surface, followedby heating at 130° C. for 2 hours to effect curing, and thereafter themold was released. Thus, as shown in FIG. 3( a), a second member 21 wasformed on the surface of the base material 23.

Subsequently, 49.5% by weight of benzyl methacrylate, 20% by weight of2-propenic acid5,5′-{4-(1,1′-biphenyl)methylene}bis[(1,1′-biphenyl)-2-poly(oxy-2,1-ethanediyl)]esterrepresented by the following structural formula (37), 30% by weight ofbisphenol-AF dimethacrylate represented by the following structuralformula (38) and 0.5% by weight of a photopolymerization initiator(IRGACURE 184, available from Ciba Speciality Chemicals Co.) were mixedto prepare an ultraviolet-curable resin composition.

(wherein y is an integer of 1 or more).

This ultraviolet-curable resin composition was dropped to thelattice-molded surface of the second member 21, and then a mold was putclose thereto from above to make the resin held full between the moldand the first member. Thereafter, this was irradiated with ultravioletrays by a high-pressure mercury lamp on the side of the second member 21to effect curing, and the mold was released. Thus, a first member 22shown in FIG. 3( b) was molded.

In this way, a close-contact double-layer type diffractive opticalelement 20 was obtained. Incidentally, the element obtained was in anouter diameter of 60 mm, a lattice height of 12 μm, and a lattice pitchof about 2 mm at the center and its vicinity and about 120 μm on theperiphery, setting pitches smaller as lattices came up to the periphery.The diffractive optical element 20 obtained according to this Examplehad the stated optical characteristics in a good precision. This wasused in an optical system to manufacture a camera. As a result, thecamera obtained was able to photograph to obtain good images that arefree of blur because of the correction of chromatic aberration by theuse of this diffractive optical element.

The refractive indexes n_(d1) and n_(d2), average dispersions MD₁ andMD₁2 and their differences n_(d1)−n_(d2) and MD₁-MD₁2 of the resin usedin each lattice member in this Example are each shown in Table 3.

POSSIBILITY OF INDUSTRIAL APPLICATION

As described above, according to the present invention, optical elementshaving superior optical characteristics can be produced. In particular,close-contact double-layer type diffractive optical elements can beproduced at a low cost and with ease.

1. An optic-purpose resin precursor composition for a close-contactdouble-layer diffractive optical element obtained by mixing at least afirst resin precursor having d-line refractive index n_(d)<1.50 and0.003<(F-line refractive index n_(F)−C-line refractive index n_(c)) inan uncured state, and a second resin precursor having d-line refractiveindex n_(d)<1.62 and 0.010<(F-line refractive index n_(F)−C-linerefractive index n_(c)) in an uncured state; said first resin precursornot containing any of a benzene ring, a sulfur atom, a chlorine atom, abromine atom and an iodine atom, and having at least one of an acrylicgroup, a methacrylic group and a vinyl group; and said second resinprecursor not containing any of a sulfur atom and a halogen atom, havingat least a cyclic structure, and having at least one of an acrylicgroup, a methacrylic group and a vinyl group.
 2. An optic-purpose resinprecursor composition for a close-contact double-layer diffractiveoptical element obtained by mixing at least a first resin precursorhaving d-line refractive index n_(d)<1.50 and 0.003<(F-line refractiveindex n_(F)−C-line refractive index n_(c)) in an uncured state, and asecond resin precursor having d-line refractive index n_(d)<1.62 and0.010<(F-line refractive index n_(F)−C-line refractive index n_(C)) inan uncured state; said first resin precursor being represented by thefollowing compositional formula (1) and having at least onepolymerizable functional group in the molecule:C_(m1)H_(n1)O_(p1)N_(q1)F_(r1)  (1) wherein m1 and n1 are each aninteger of 5 or more, p1 and q1 are each an integer of 0 or 1 or moreand ml or less, and r1 is an integer of 0 or 1 or more and (n1×2) orless; and said second resin precursor being represented by the followingcompositional formula (2) and having at least one polymerizablefunctional group in the molecule and at least one benzene ring in themolecule:C_(s)H_(t)O_(u)N_(v)  (2)  wherein s and t are each an integer of 5 ormore, and u and v are each an integer of 0 or 1 or more and s or less.3. The optic-purpose resin precursor composition according to claim 2,wherein said polymerizable functional group is an acrylic group or amethacrylic group.

wherein R¹, R³, R⁵, R⁷, R¹² and R¹⁷ are each a hydrogen atom or a methylgroup; R², R⁴ and R⁶ are each a monovalent organic group; R⁸ is adivalent organic group; R⁹ to R¹¹ are each a monovalent organic grouphaving an acrylic group or a methacrylic group; R¹³, R¹⁴ and R¹⁶ areeach a divalent organic group; R¹⁵, R¹⁸ and R¹⁹ are each a monovalentorganic group; a, d and f are each a number of 2 or more to 4 or less;and b, e and g are each 1 or more; and said second resin precursor is acompound represented by any of the following general formulas (10) to(12).
 4. The optic-purpose resin precursor composition according toclaim 1, wherein said first resin precursor is a compound represented byany of the following general formulas (3) to (9):

wherein R²⁰ and R²² are each a hydrogen atom or a methyl group; R²¹ andR²³ are each a divalent organic group; Z¹ is a divalent organic grouphaving a ring structure, Z² is a trivalent organic group, and h and iare each an integer.
 5. An optic-purpose resin obtained by curing theoptic-purpose resin precursor composition according to claim
 4. 6. Theoptic-purpose resin according to claim 5, which has d-line refractiveindex n_(d)<1.55 and (F-line refractive index n_(F)−C-line refractiveindex n_(c))>0.010.
 7. An optical element comprising a first membercomprising the resin according to claim
 6. 8. The optical elementaccording to claim 7, which further comprises a second member joined tosaid first member in close contact; a d-line refractive index nd₁ ofsaid second member being larger than a d-line refractive index n_(d2) ofsaid first member, and a difference found by subtracting a C-linerefractive index n_(C1) of said second member from an F-line refractiveindex n_(F1) of said second member being smaller than a difference foundby subtracting a C-line refractive index n_(C2) of said first memberfrom an F-line refractive index n_(F2) of said first member.
 9. Theoptical element according to claim 8, wherein said second member is aglass having a glass transition temperature lower than 400° C.
 10. Aclose-contact double-layer diffractive optical element comprising asecond member formed of a first resin and a first member formed of asecond resin, joined to the second member in close contact; a d-linerefractive index n_(d1) of said second member being larger than a d-linerefractive index n_(d2) of said first member; an average dispersion MD₁of said second member which is found by subtracting a C-line refractiveindex n_(C1) from an F-line refractive index n_(F1) of said secondmember being smaller than an average dispersion MD₂ of said first memberwhich is found by subtracting a C-line refractive index n_(C2) from anF-line refractive index n_(F2) of said first member; and said firstresin having an alicyclic structure in the repeating unit.
 11. Theoptical element according to claim 10, wherein said first resin containsat least one of an alicyclic olefin resin, an alicyclic acrylic resin,an alicyclic polyurethane resin, a resin having an episulfide structureand an epoxy-acrylate resin having structure.
 12. The optical elementaccording to claim 11, wherein said second resin has both a benzene ringand a fluorine atom in the repeating unit.
 13. A close-contactdouble-layer type diffractive optical element comprising a second memberformed of a first resin and a first member formed of a second resin,joined to the second member in close contact; a d-line refractive indexn_(d1) of said second member being larger than a d-line refractive indexn_(d2) of said first member; an average dispersion MD₁ of said secondmember which is found by subtracting a C-line refractive index n_(C1)from an F-line refractive index n_(F1) of said second member beingsmaller than an average dispersion MD₂ of said first member which isfound by subtracting a C-line refractive index n_(C2) from an F-linerefractive index n_(F2) of said first member; and said second resinhaving both a benzene ring and a fluorine atom in the repeating unit.14. The optical element according, to claim 12, wherein said secondresin does not contain any of a sulfur atom, a chlorine atom, a bromineatom and an iodine atom in the molecule.
 15. The optical elementaccording to claim 14, wherein said second resin is anultraviolet-curable resin.
 16. The optical element according to claim11, wherein the d-line refractive index n_(d1) of said second member is1.45 or more; and the average dispersion MD₁ of said second member is0.02 or less.
 17. The optical element according to claim 12, wherein thed-line refractive index n_(d2) of said first member is 1.60 or less; andthe average dispersion MD₂ of said first member is 0.01 or more.
 18. Theoptical element according to claim 16, wherein a difference found bysubtracting the d-line refractive index n_(d2) of said first member fromthe d-lime refractive index n_(d1) of said second member is 0.03 ormore; and a difference found by subtracting the average dispersion MD₂of said first member from the average dispersion MD₁ of said secondmember is −0.003 or less.
 19. A close-contact double-layer diffractiveoptical element comprising a second member formed of a first resin and afirst member formed of a second resin, joined to the second member inclose contact; a d-line refractive index n_(d1) of said second memberbeing larger than a d-line refractive index n_(d2) of said first member;an average dispersion MD₁ of said second member which is found bysubtracting a C-line refractive index n_(C1) from an F-line refractiveindex n_(Fl) of said second member being smaller than an averagedispersion MD₂ of said first member which is found by subtracting aC-line refractive index n_(C2) from an F-line refractive index n_(F2) ofsaid first member; said first resin having an alicyclic structure in therepeating unit and containing at least one of an alicyclic olefin resin,an alicyclic acrylic resin, an alicyclic polyurethane resin, a resinhaving an episulfide structure and an epoxy-acrylate resin havingstructure; said second resin having both a benzene ring and a fluorineatom in the repeating unit and not containing any of a sulfur atom, achlorine atom, a bromine atom and an iodine atom in the molecule; andsaid first member comprises the optic-purpose resin according to claim6.
 20. An optical article comprising the optical element according toclaim
 19. 21. A method for producing a close-contact double-layerdiffractive optical element having a second member formed of a firstresin and a first member formed of a second resin, joined to the secondmember in close contact, wherein said method has the step of molding aprecursor composition of said first resin and curing the composition toform said second member; said first resin has an alicyclic structure inthe repeating unit; a d-line refractive index n_(d1) of said first resinis larger than a d-line refractive index n_(d2) of said second resin;and an average dispersion MD₁ of said first resin which is found bysubtracting a C-line refractive index n_(C1) from an F-line refractiveindex n_(F1) of said first resin is smaller than an average dispersionMD₂ of said second resin which is found by subtracting a C-linerefractive index n_(C2) from an F-line refractive index n_(F2) of saidsecond resin.
 22. A method for producing a close-contact double-layerdiffractive optical element having a second member formed of a firstresin and a first member formed of a second resin, joined to the secondmember in close contact, wherein said method has the step of molding aprecursor composition of said second resin and curing the composition toform said first resin; said second resin has both a benzene ring and afluorine atom in the repeating unit; a d-line refractive index n_(d2) ofsaid second resin is smaller than a d-line refractive index n_(d1) ofsaid first resin; and an average dispersion MD₂ of said second resinwhich is found by subtracting a C-line refractive index n_(C2) from anF-line refractive index n_(F2) of said second resin is larger than anaverage dispersion MD₁ of said first resin which is found by subtractinga C-line refractive index n_(C1) from an F-line refractive index n_(F1)of said first resin.
 23. The optic-purpose resin precursor compositionaccording to claim 2, wherein said first resin precursor is a compoundrepresented by any of the following general formulas (3) to (9):

wherein R¹, R³, R⁵, R⁷, R¹² and R¹⁷ are each a hydrogen atom or a methylgroup; R², R⁴ and R⁶ are each a monovalent organic group; R⁸ is adivalent organic group; R⁹ to R¹¹ are each a monovalent organic grouphaving an acrylic group or a methacrylic group; R¹³, R¹⁴ and R¹⁶ areeach a divalent organic group; R¹⁵, R¹⁸ and R¹⁹ are each a monovalentorganic group; a, d and f are each a number of 2 or more to 4 or less;and b, e and g are each 1 or more; and said second resin precursor is acompound represented by any of the following general formulas (10) to(12):

 wherein R²⁰ and R²² are each a hydrogen atom or a methyl group; R²¹ andR²³ each a divalent organic group; Z¹ is a divalent organic group havinga ring structure; Z² is a trivalent organic group, and h and i are eachan integer.
 24. An optic-purpose resin obtained by curing theoptic-purpose resin precursor composition according to claim
 23. 25. Theoptic-purpose resin according to claim 24, which has d-line refractiveindex n_(d)<1.55 and (F-line refractive index n_(F)−C-line refractiveindex n_(c))<0.010.
 26. An optical element comprising a first membercomprising the resin according to claim
 25. 27. The optical elementaccording to claim 26, which further comprises a second member joined tosaid first member in close contact; a d-line refractive index n_(d1) ofsaid second member being larger than a d-line refractive index n_(d2),of said first member, and a difference found by subtracting a C-linerefractive index n_(C1) of said second member from an F-line refractiveindex n_(F1) of said second member being smaller than a difference foundby subtracting a C-line refractive index n_(C2) of said first memberfrom an r-line refractive index n_(F2) of said first member.
 28. Theoptical element according to claim 13, wherein said second resin doesnot contain any of a sulfur atom, a chlorine atom, a bromine atom and aniodine atom in the molecule.
 29. The optical element according to claim28, wherein said second resin is an ultraviolet-curable resin.
 30. Theoptical element according to claim 13, wherein the d-line refractiveindex n_(d2) of said first member is 1.60 or less; and the averagedispersion MD₂ of said first member is 0.01 or more.
 31. The opticalelement according to claim 17, wherein a difference found by subtractingthe d-line refractive index n_(d1) of said second member is 0.03 ormore; and a difference found by subtracting the average dispersion MD₂of said first member from the average dispersion MD₁ of said secondmember is −0.003 or less.
 32. The optical element according to claim 30,wherein a difference found by subtracting the d-line refractive indexnd₂ of said first member from the d-line refractive index n_(d1) of saidsecond member is 0.03 or more; and a difference found by subtracting theaverage dispersion MD₂ of said first member from the average dispersionMD₁ of said second member is −0.003 or less.
 33. A close-contactdouble-layer diffractive optical element comprising a second memberformed of a first resin and a first member formed of a second resin,joined to the second member in close contact; a d-line refractive indexn_(d1) of said second member being larger than a d-line refractive indexn_(d2) of said first member; an average dispersion MD₁ of said secondmember which is found by subtracting a C-line refractive index n_(C1)from an F-line refractive index n_(F1) of said second member beingsmaller than an average dispersion MD₂ of said first member which isfound by subtracting a C-line refractive index n_(C2) from an F-linerefractive index n_(F2) of said first member; said second resin havingboth a benzene ring and a fluorine atom in the repeating unit but notcontaining any of a sulfur atom, a chlorine atom, a bromine atom and aniodine atom in the molecule; and, said first member comprises theoptic-purpose resin according to claim
 6. 34. A close-contactdouble-layer diffractive optical element comprising a second memberformed of a first resin and a first member formed of a second resin,joined to the second member in close contact; a d-line refractive indexn_(d1) of said second member being larger than a d-line refractive indexn_(d2) of said first member; an average dispersion MD₁ of said secondmember which is found by subtracting a C-line refractive index n_(C1)from an F-line refractive index n_(F1) of said second member beingsmaller than an average dispersion MD₂ of said first member which isfound by subtracting a C-line refractive index n_(C2) from an F-linerefractive index n_(F2) of said first member; said first resin having analicyclic structure in the repeating unit, containing at least one of analicyclic olefin resin, an alicyclic acrylic resin, an alicyclicpolyurethane resin, a resin having an episulfide structure and anepoxy-acrylate resin having structure; said second resin having both abenzene ring and a fluorine atom in the repeating unit but notcontaining any of a sulfur atom, a chlorine atom, a bromine atom and aniodine atom in the molecule; and, said first member comprises theoptic-purpose resin according to claim
 25. 35. A close-contactdouble-layer diffractive optical element comprising a second memberformed of a first resin and a first member formed of a second resin,joined to the second member in close contact; a d-line refractive indexn_(d1) of said second member being larger than a d-line refractive indexn_(d2) of said first member; an average dispersion MD₁ of said secondmember which is found by subtracting a C-line refractive index n_(C1)from an F-line refractive index n_(F1) of said second member beingsmaller than an average dispersion MD₂ of said first member which isfound by subtracting a C-line refractive index n_(C2) from an F-linerefractive index n_(F2) of said first member; said second resin havingboth a benzene ring and a fluorine atom in the repeating unit but notcontaining any of a sulfur atom, a chlorine atom, a bromine atom and aniodine atom in the molecule; and, said first member comprises theoptic-purpose resin according to claim
 25. 36. An optical articlecomprising the optical element according to claim
 33. 37. An opticalarticle comprising the optical element according to claim
 34. 38. Anoptical article comprising the optical element according to claim 36.